The present invention relates to a projection exposure apparatus and method. The apparatus and method may be used, for example, in a photolithographic process which forms a part of a fabrication process of semiconductor devices, liquid crystal displays or other products, in exposing a mask pattern on a substrate, such as a wafer.
In a photolithographic process for fabricating semiconductor devices or other products, there have been used various projection exposure apparatus including stepping projection exposure apparatus called stepping projection aligners or steppers, as well as scanning projection exposure apparatus called scanning projection aligners or step-and-scan projection aligners. These projection exposure apparatus use a projection optical system (or projection lens) which has to provide an extremely high resolution approaching the theoretical resolution limit. In order to support such a high resolution, many projection optical systems have certain mechanisms for measuring various factors in the resolution (such as, the atmospheric pressure and the ambient temperature) and then correcting the image formation characteristics of the projection optical system depending on the result of such measurement. For higher resolution, projection optical systems are designed to have a large numerical aperture. As a result, the depth of focus is very small. Thus, many projection optical systems have a autofocus mechanism which may comprise an oblique-incidence focus position detection system (or AF sensor). The AF sensor serves to measure the focus position (or the position in the direction along the optical axis of the projection optical system) of the surface of a wafer (or substrate) which typically has some irregularities. The autofocus mechanism brings the surface of the wafer into a position at which it will be coincident with the image plane of the projection optical system, based on the result of such measurement.
In recent years, image formation errors caused by deformation of a mask or reticle have become a problem. If substantially all the pattern-bearing surface area of a reticle is deformed down toward the projection optical system, the average position of the image plane (or image surface) of the pattern-bearing surface is displaced downward, so that the focus position of a wafer could suffer from defocusing if it were not adjusted. Further, when the pattern-bearing surface of a reticle is deformed, the positions of the pattern, which are perpendicular to the optical axis of the projection optical system, on the pattern-bearing surface may also is displaced. Such lateral displacements (or displacements in the direction perpendicular to the optical axis of the projection optical system) may cause distortion errors.
Further, regarding the demagnification projection optical system used in various demagnification projection exposure apparatus including those of non-scan-type (such as, steppers) and those of scan-type (such as, step-and-scan projection aligners), there is an urgent need for improvement in characteristics relating to a reduction in lens aberrations. In the state of the art, almost all lens aberrations could be highly suppressed if lenses were manufactured accurately to design specifications. However, in fact, due to accumulation of tolerances and allowances necessary for fabricating the lenses, the image formation characteristics of the finished lenses are limited and include errors.
There have been many proposals to reduce lens aberrations contributed to by factors involved in the fabrication process. One such technique uses one or more aberration correction plates disposed between the projection optical system and the wafer (or glass substrate), for canceling out the aberrations. Specifically, any residual aberrations which remain after final adjustment of a lens are canceled out by the reverse aberrations intentionally produced by the aberration correction plates so as to minimize the resultant lens aberrations. The residual aberrations may be determined by making and analyzing a test. print using that lens together with a test reticle having evaluation patterns formed thereon, or by measuring the position of aerial images of evaluation patterns of a test reticle formed by that lens by means of a measuring photodetector.
There have been further factors affecting the final image formation characteristics of a lens, which relate to the accuracy (or drawing errors) in the evaluation patterns of a test reticle. In particular, the patterning accuracy (including the linewidth accuracy) of a test reticle is of great concern. In order to correct errors arising from insufficient patterning accuracy, a system has been used in which the pattern positions (or the distances between the patterns) of a finished test reticle are measured and stored using a precision coordinate measurement device, and the positions of the projected images are corrected by an utilization of the stored pattern positions.
As described above, when the image formation characteristics of a projection optical system are evaluated, measurement errors due to insufficient patterning accuracy of an evaluation reticle may be corrected by an utilization of the pattern positions which are measured and stored in advance. However, there are further structural factors affecting the final or total image formation characteristics of the projection exposure apparatus, including the flatness of the exposure area of an evaluation reticle, flatness of the area outside the exposure area of a reticle, and the deflection of a reticle when it is loaded on the projection exposure apparatus. In the past when requirements for the image formation characteristics were less severe, the need for various accuracies relating to these structural factors did not arise. However, in recent years, requirements for the patterning accuracy of semiconductor chips and the registration accuracy between layers of the semiconductor chips have become very severe, so that the accuracies relating to the above structural factors have become of more significance in order to meet such requirements.
One of the structural factors, the deflection of a reticle when it is loaded on the projection exposure apparatus, is caused by gravity. Typically, a reticle is supported at three or four points over its peripheral area and secured by means of vacuum suction, which invariably causes some deflection. When the reticle is curved by deflection, the features of the pattern on the reticle are laterally displaced thereby, the projected images of the features are laterally displaced from their desired positions on the wafer. Apart from the deflection, since each reticles is different in its flatness, if there is a poor flatness in the reticles, the images of the features may be projected features off their desired positions on the wafer. Further, there are sometimes big difference in its flatness between the exposure area and the peripheral area outside the exposure area, and in particular, the peripheral area may typically have a poor flatness. In such a case, since the reticle is supported and secured at the peripheral area, the flatness of the reticle may be possibly deteriorated. This results in larger lateral displacements of the projected images depending on the matching between the contact surfaces of the reticle and the projection exposure apparatus.
FIG. 30(A) shows how a reticle or mask 900 is supported at its peripheral area by a mask holder 902. The contact surfaces of the mask holder 902 in contact with the mask 900 have holes or grooves 904 for securing the mask 900 onto the mask holder 902. When the holes or grooves 904 are in communication with a vacuum source, the mask 900 is secured t the onto the mask holder 902 by vacuum suction.
However, holding a mask on a mask holder in this manner suffers from a problem that the mask 900 is deflected by the gravity as shown in FIG. 30(A). This results in the lateral displacements of the features of the pattern formed on the mask 900 as well as the curve of the image surface defined by the projection optical system. Further, irradiation of the exposure light rays onto the mask 900 during exposure operations imparts irradiation heat to the mask 900 and increases its temperature, this results in the thermal expansion of the mask 900. Since the mask 900 is secured at its peripheral area onto the mask holder 902, the mask 900 is deformed as shown in FIG. 30(B). As the result, the pattern on the mask 900 is also deformed, which may disadvantageously produce variation In the distortion of the projected pattern image and/or add to the curvature of the image surface so that the depth of focus in the pattern-bearing surface of the mask become inconveniently smaller. With today""s highly miniaturized patterns, even a minute deformation of the pattern can be of great concern.
Apart from deflection caused by gravity, the deformation of a mask or reticle may be also caused In the polishing process of the glass plate forming the reticle, or may be caused depending on insufficient flatness of one or both of the contact surfaces of the reticle and the reticle holder, which are forced to come into contact with each other by vacuum suction. Since there is difference in the deflections between reticles, or between projection exposure apparatus, a deflection of a particular reticle has to be measured when it is held on the reticle holder of a particular projection exposure apparatus in order to obtain an accurate reticle deformation.
One method for measuring the deformation of the pattern-bearing surface of a reticle held on the reticle holder of a projection exposure apparatus by vacuum suction may comprise the steps of making and analyzing a test print using the projection optical system of that projection exposure apparatus. The selected features of the pattern formed on the pattern-bearing surface of the reticle are projected through the projection optical system onto a wafer for evaluation. This projection exposure is repeated while the focus position of the wafer is varied in a stepwise manner. After the development process of the resist layer on the wafer, the resist patterns thus formed are examined for their contrast, and the exposure specifications for the resist patterns of the highest contrast among those corresponding to the same features of the reticle pattern indicate the best-focus positions of the projected images of the respective features of the reticle pattern. Then, from the displacements of the best-focus positions, the deformation of the pattern-bearing surface of the reticle may be calculated quantitatively to a certain extent.
As described above, in order to achieve better image formation characteristics of a projection exposure apparatus, it is preferable to measure not only. the surface shape of the wafer loaded thereon but also the surface shape of the pattern-bearing surface of the reticle. Nevertheless, any test-print method, in which a test print is made for measuring the surface shape, is time-consuming and thus often results in a poor throughput of the exposure process. In addition, any reticle used for actual exposure process has a pattern to be transferred onto wafers (thus, no test pattern), so that any test-print method can not be applied to the reticles for use in actual exposure process. Another option to quickly perform measurement of the surface shape of the pattern-bearing surface of a reticle is to use such an oblique-incidence position sensor disposed around the reticle stage, that has the same arrangement as a commonly used, oblique-incidence AF sensor for detecting the focus position of a wafer.
Since a reticle has a pattern-bearing surface defined on its bottom surface facing down toward the projection optical system, the position of the oblique-incidence position sensor would be disposed in the space between the reticle stage and the projection optical system or around that space. However, a reticle often has a pellicle stretched on a metal frame provided on the bottom surface of the reticle, for preventing any foreign particles from adhering onto the pattern-bearing surface of the reticle. In such a case, the position sensor is prevented from projecting the detection light beam onto the pattern-bearing surface of the reticle at a nearly grazing angle (or at a large angle of incidence) by the pellicle frame.
In particular, for a scanning projection exposure apparatus, since the reticle stage used therein has to show sufficient rigidity to prevent any harmful deformation when accelerated/decelerated for movement in synchronism with the wafer stage for scanning, the reticle stage is generally given a sufficient thickness, thereby usually the bottom surface of the reticle is close to the upper end of the projection optical system. Further, the smaller the space distance between the reticle and the projection optical system, the easier the projection optical system may be designed, so that projection optical systems having a greater precision tend to provide less space between the reticle and the projection optical system. Thus, it is difficult to dispose a position sensor for measuring the surface shape of a reticle in the space between the projection optical system and the reticle.
Moreover, a position sensor for measuring the surface shape of a reticle must have a high stability against aging. This is because even such a variation in measurements provided from the position sensor, that is actually caused by aging, is interpreted as indicating a variation in the surface shape of the reticle, leading to an erroneous correction of the image formation characteristics.
Regarding the reticle itself, it may comprise a thin plate of silica glass having one surface (the bottom surface when used) covered with thin-film of chromium deposited thereon. Typical sizes of reticles include 5xc3x975 inches (127xc3x97127 mm) and 6xc3x976 inches (152xc3x97152 mm), while typical thicknesses include 0.09 inches (2.3 mm) and 0.25 inches (6.4 mm).
FIG. 31 is a plan view of a typical reticle showing the planar layout of the parts and features of the reticle. As shown, the reticle R has its central portion defined as a pattern area 933 in which a semiconductor chip circuit pattern is formed. The peripheral area 931 surrounding the pattern area 933 includes a pellicle frame attachment area 932 at the innermost portion of the peripheral area 931. A pellicle frame is attached on the reticle R in the pellicle frame attachment area 932. The pellicle frame supports a pellicle stretched thereon, which is a thin film of a suitable organic material for covering the pattern area to prevent any foreign particle from adhering to the pattern-bearing surface. Out of the pellicle frame attachment area 932 and right and left sides thereof as viewed in FIG. 31, there are formed support portions 935 at which the reticle R is supported and secured on the reticle holder by vacuum suction, as well as formed alignment marks AM.
As shown in FIG. 32, the reticle R my be deflected downward by the gravity. The maximum downward displacement at the center of the reticle R may be several micrometers (xcexcm). This deflection produces not only displacements of the features of the pattern in the focus direction (or the direction of the optical axis of the projection optical system) but also lateral displacements of the features. The lateral displacement increases as the feature lies father off the center of the reticle R, so that the displacements produce an distortion error. The maximum lateral displacement may be of the order of 0.01 xcexcm.
In the case where the reticle support portions 943 for supporting the reticle R thereon are formed as vacuum chucks, the deflection of the reticle R by the gravity may be suppressed by the corrective forces acting from the top surfaces of the reticle support portions 943, when the top surfaces are level or extend horizontally. However, since the recent years"" projection lenses have a very high numerical aperture with a extremely small depth of focus, and there is the need for the improvement of the overlay accuracy in order to support the more and more reducing linewidth, even a relatively low level of residual deformations of reticles after the correction by the corrective forces by vacuum chucks may arise a problem.
As regards the reticles used for exposure of silicon wafers, 5-in. square reticles are being replaced by 6-in. square reticles. Simultaneously, reticles of 0.09-in. in thickness are being replaced by those of 0.25-in. in thickness for the purpose of reducing any errors which may occur due to the deformation of reticles. In view of recent trends in the semiconductor device industry, greater exposure fields and greater reticle sizes are expected to be required and become common in the near future. The expected next generation of reticles are 9-in. square reticles, for which the thickness of about 0.5 in. would be required in order to meet both a focus condition of xc2x10.1 mm and a distortion tolerance or 0.005 mm. It is expected that 9-in. square reticles would become common in 2000 A.D., where scanning projection exposure machines in which a reticle and a wafer are moved in synchronism with each other would be the prevailing exposure machines. A reticle of a greater thickness means a heavier reticle, which may arise a problem regarding the secure holding of a reticle by the reticle holder since a reticle must be accelerated and decelerated for scanning projection exposure. Further, for enhancing the throughput, high speed operations of exposure machines are required, which would lead to a limitation on the weight of a reticle. Thus, the thickness of a reticle should be a compromise between the anti-deflection and throughput requirements, which may not be ideal in view of the anti-deflection capability. Accordingly, it is difficult to meet both the desired focus condition and distortion tolerance with any of conventional techniques.
The first object of the present invention is to provide a projection exposure apparatus capable of making a projection exposure of a mask pattern in a convenient manner.
The second object of the present invention is to provide a projection exposure method with which improved image formation characteristics may be obtained even if a reticle (mask) has a poor flatness, as well as to provide a projection exposure apparatus with which such method may be conveniently performed.
The third object of the present invention is to provide a scanning projection exposure method with which a pattern-bearing surface of a reticle may be well measured and thereby improved image formation characteristics may be obtained even if there is little space between a reticle stage and a projection optical system and thus it is difficult to dispose in that space a sensor for measuring the surface shape of the pattern-bearing surface of the reticle, as well as to provide a scanning projection exposure apparatus with which such method may be conveniently performed.
The fourth object of the present invention is to provide projection exposure apparatus and method with which the thickness and weight of a reticle may be suppressed and any pattern transfer errors due to the deformation of the reticle may be eliminated.
In order to achieve the above-mentioned first object, in accordance with the present invention, there is provided a projection exposure apparatus for projecting an image of a pattern formed on a mask onto an object of exposure, comprising: a deflection detection device for detecting deflection of the mask; a deflection correction device for correcting deflection of the mask; an arithmetic device for calculating a deflection correction value for the deflection correction device based on the detection result obtained by the deflection detection device; and a control device for controlling the deflection correction device in accordance with the deflection correction value calculated by the arithmetic device.
In several embodiments of significance, the deflection detection device comprises: a light-beam-projecting device for obliquely projecting a light beam onto the mask; and a light-beam-detecting device for detecting a reflected light beam projected by the light-beam-projecting device and reflected by the mask so as to produce a detection signal corresponding to the variation in the position at which the reflected light beam is received. Further, the deflection correction device may correct deflection of the mask by changing pneumatic pressure, or alternatively, the deflection correction device may correct deflection of the mask by operating a piezoelectric actuator element.
In accordance with this aspect of the present invention, any deflection of the mask produced by the gravity and/or the thermal expansion is detected by, for example, an oblique-incidence detection system. Based on the detection result, a deflection correction value is calculated and the deflection is corrected. As the result, any curvature of the pattern image is suppressed and an accurate and stable image of the mask pattern may be obtained. In several embodiments of significance, the deflection of the mask is corrected and any variation in the projected image is corrected by changing pneumatic pressure or operating a piezoelectric actuator element.
In order to achieve the above-mentioned second object, in accordance with the present invention, there is provided a projection exposure method for making a projection exposure of an image of a pattern formed on a mask through a projection optical system onto a substrate, comprising the steps of: measuring and. storing a surface shape of a pattern-bearing surface of the mask; and making an exposure while partially correcting, based on the surface shape as stored, the position at which an image of the pattern of the mask is formed through the projection optical system.
With this projection exposure method, for example, a correction mechanism may be used for correcting image formation characteristics including the distortion by driving one or some of the lens elements of the projection optical system. Further, for example, by using a distortion evaluation mask having evaluation patterns formed thereon, the positions of projected images of the evaluation patterns are measured so as to determine the distortion actually produced by the projection optical system. However, the determined distortion contains error components due to lateral displacements of features of the pattern on the pattern-bearing surface produced by the deformation of the surface shape thereof. Therefore, from the measured surface shape of the pattern-bearing surface of the distortion evaluation mask, a distribution of expected displacements of projected images of the evaluation patterns from their desired projection positions is calculated. Then, the measurements of the distortion is adjusted with the expected displacements so as to derive a distortion to be produced solely by the projection optical system. In the actual exposure process, the surface shape of the mask for the actual exposure process is measured, and the measurement result is used to calculate the expected lateral displacements of the points in the projected image which are expected to be produced by the surface shape. Then, the expected displacement of the projected image is added to the distortion which is produced solely by the projection optical system so as to derive a total expected distortion. The correction mechanism corrects the total expected distortion, so that excellent image formation characteristics may be obtained even when the mask has irregularities in its surface or suffers from tilt.
This projection exposure method may be also applied to projection exposure apparatus of the type called step-and-scan projection aligners, in which the surface shape of a mask may possibly vary depending on the position on the mask in the scanning direction, so that the distortion correction value has to be varied while the mask is moved for scanning. In such a case, the correction mechanism may control the distortion correction value depending on the position of the mask during an scanning projection exposure operation, so that excellent image formation characteristics may be obtained over the entire region in the scanning direction. Further, in such a case, if the distortion of the projection optical system has been well corrected, the distortion correction may be performed such that only the lateral displacements of the points in the projected image which are produced by the surface shape of the pattern-bearing surface of the mask may be canceled out.
In order to achieve the above-mentioned second object, in accordance with the present invention, there is also provided another projection exposure method for making a projection exposure of an image of a pattern formed on a mask through a projection optical system onto a substrate, the mask being supported by a predetermined support member, comprising the steps of: measuring and storing any irregularities (including tilt) in a contact surface of the mask in contact with the support member; and making an exposure while partially correcting, based on the irregularities in the contact surface as stored, the position at which an image of the pattern of the mask is formed through the projection optical system.
With this projection exposure method, the mask may be secured onto the support member by vacuum suction. In such a case, if the contact surfaces (245A to 245D) of the mask which are in contact with the support member are tilted as shown in FIG. 17(B), the mask is caused to curve as shown in FIG. 17(C) when it is secured by the vacuum suction, so that the flatness of the mask is deteriorated. This problem may be solved by: determining, based on any irregularities in the contact surfaces between the mask and the support member, an expected variation in the irregularities in the contact surface of the mask which is expected to be produced when the mask is secured onto the support member by vacuum suction; adjusting the measurement result of the distortion of the projection optical system by the expected lateral displacement of the projected image; and correcting the image formation characteristics based on the adjusted distortion, so that excellent image formation characteristics may be obtained.
In order to achieve the above-mentioned second object, in accordance with the present invention, there is also provided further another projection exposure method for making a projection exposure of an image of a pattern formed on a mask through a projection optical system onto a substrate, the mask being supported by a predetermined support member, comprising the steps of: measuring and storing any irregularities (including tilt) in a contact surface of the support member in contact with the mask; and making an exposure while partially correcting, based on the irregularities in the contact surface as stored, the position at which an image of the pattern of the mask is formed through the projection optical system. With this projection exposure method, if the contact surfaces of the support member in contact with the mask are tilted, the mask is caused to curve as shown in FIG. 17(A) when it is secured by the vacuum suction onto the contact surfaces. This problem may be solved by: determining an expected variation in the irregularities in the surface of the mask which is expected to be produced when the mask is secured onto the support member by vacuum suction; and correcting the measurements of the distortion of the projection optical system based on the expected variation thus determined, so that excellent image formation characteristics may be obtained.
In order to achieve the above-mentioned second object, in accordance with the present invention, there is also provided a projection exposure apparatus for making a projection exposure of an image of a pattern formed on a mask through a projection optical system onto a substrate, comprising: a measurement system for measuring a surface shape of a pattern-bearing surface of the mask: a storage for storing data representing the surface shape measured by the measurement system; an image formation characteristics correction system for partially correcting the position at which an image of the pattern of the mask is formed through the projection optical system: and a control system for making an exposure while correcting, through the image formation characteristics correction system and based on the data in the storage representing the surface shape, the position at which an image of the pattern of the mask is formed through the projection optical system. With this projection exposure apparatus, the projection exposure methods described above for achieving the above-mentioned second object may be conveniently performed.
In order to achieve the above-mentioned third object, in accordance with the present invention, there is provided a scanning projection exposure method in which a mask and a substrate are moved in synchronism with each other for transferring a pattern formed on the mask through a projection optical system onto the substrate, comprising the steps of: measuring a surface shape of a pattern-bearing surface of the mask, prior to making a scanning projection exposure of the substrate with the pattern of the mask; and correcting at least one of 1) image formation characteristics of the projection optical system and 2) the position of the substrate, based on the measurement result of the pattern-bearing surface, while making a scanning projection exposure.
With this scanning projection exposure method, the surface shape of the pattern-bearing surface of the mask can be measured while at least a part of the pattern-bearing surface is in an area outside a transfer area to be transferred by the projection optical system, so that the sensor for measuring the surface shape of the mask may be disposed at a position away from the projection optical system to the scanning direction. Accordingly, the sensor may be disposed with ease even when there is little space between the projection optical system and the mask stage and be used to measure the deformation (or the deflection) of the mask. Either the image formation characteristics of the projection optical system or the position of the substrate may be corrected based on the measured deformation, so that excellent image formation characteristics may be obtained.
With this method, it is preferable to perform the measurement of a surface shape of the pattern-bearing surface of the mask while the mask stands still at a starting point for scanning or while the mask is being accelerated for scanning. That is, when a mask replacement is done, by measuring a surface shape of the pattern-bearing surface of the new mask once while the pattern-bearing surface of the new mask is at a starting point for scanning or in an acceleration region, the necessary correction may be made during the subsequent exposure operation. Further, in the case where the surface shape measurement is performed in the acceleration region, it is unnecessary to extend the stroke of the movement of the mask for the surface shape measurement. Moreover, the measurement of a surface shape of the mask may be alternatively performed while the mask is being scanned for exposure, while the mask is being decelerated after scanning, or while the mask stands still after deceleration.
In order to achieve the above-mentioned third object, in accordance with the present invention, there is also provided a scanning projection exposure apparatus in which a mask and a substrate are moved in synchronism with each other for transferring a pattern formed on the mask through a projection optical system onto the substrate, comprising: a shape measurement system defining a plurality of detection points in an area outside a transfer area to be transferred by the projection optical system, for measuring a surface shape of a pattern-bearing surface of the mask; and a correction system for correcting at least one of 1) image formation characteristics of the projection optical system and 2) the position of the substrate, based on the measurement result by the shape measurement system.
With this scanning projection exposure apparatus, the shape measurement system may be disposed at a position away from the projection optical system to the scanning direction, and may be used to measure the surface shape of the pattern-bearing surface of the mask with ease. Further, the mask may be scanned along the shape measurement system, so that the surface shape of the entire pattern-bearing surface of the mask may be measured. With this exposure apparatus, the scanning projection exposure method described above for achieving the above-mentioned third object may be conveniently performed.
It is preferable to form a reference surface on a mask stage for moving the mask, such that the reference surface may be substantially level with the pattern-bearing surface of the mask. In such a case, at first the measurement by the shape measurement system is performed by measuring the position of the reference surface, and then measuring the surface position of the reticle with reference to the measured position of the reference surface. That is, the differential between the reference surface and the surface position of the mask is measured. By virtue of this, it is sufficient for the shape measurement system to have such stability for a very short time from when the reference surface has been measured to when the surface of the mask has been measured. Thus, even if the measurements produced from the shape measurement system tend to fluctuate within a certain period, the expected variation in the image formation characteristics may be determined with precision so as to make an appropriate correction for the variation.
In these cases, it is also preferable to perform the measurement of a surface shape of the pattern-bearing surface of the mask while the mask stands still at a starting point for scanning or while the mask is being accelerated for scanning.
In order to achieve the above-mentioned fourth object, in accordance with the present invention, there is provided a projection exposure apparatus, comprising: a first holder for holding a master matrix; an illumination optical system for illuminating the master matrix; a projection optical system for focusing light rays which pass through the master matrix on a photosensitized substrate so as to form an image thereon; and a second holder for holding the photosensitized substrate; wherein error factors due to the deformation of the master matrix produced by the gravity when the master matrix is held on the first holder have been corrected through a design process of a projection lens.
In stead of, or in addition to, the correction of the errors through the design process of the lens, an adjustment mechanism for the projection lens may be used to correct the errors in an adjustment process for the apparatus.
In order to achieve the above-mentioned fourth object, in accordance with the present invention, there is also provided a projection exposure method for making a projection exposure of a pattern on a master matrix onto a photosensitized substrate to transfer the pattern onto the substrate, comprising the step of: correcting, through a design process of a projection lens, error factors due to the deformation of the master matrix produced by the gravity when the master matrix is held.
That is, any focus errors and distortion errors which are expected to be produced by the deflection of a reticle are corrected through a reticle design process or an adjustment process. Therefore, any pattern transfer errors due to the deformation of a reticle may be eliminated even when the reticle has a relatively small thickness.
With this projection exposure method, it is preferable to determine errors due to the deformation of the master matrix produced by the gravity, through an exposure process or a measurement process performed using a reference master matrix, and adjust a projection lens of the projection optical system such that the errors may be eliminated, and then make an actual exposure. In this case, any errors are determined and corrected through the adjustment process, so that even the error produced by the reticle chucks may be determined and corrected.